Sure, Donald Trump has the support of David Duke. But the membership of the Ku Klux Klan is small. So anyone hoping to understand Trump's electoral appeal must assume it goes beyond those whose favorite pastime is burning crosses.

Rep. Chris Collins, R-N.Y., recently explained why he endorsed the GOP front-runner. "I come from an interesting rural county with a lot of Rust Belt union folks, and Donald Trump is truly resonating through western New York," he told The New York Times. "It starts first and foremost with the leader who is going to make our borders safe again."

His district is actually on the border -- the border with Canada. But that's not the one Trump wants to secure with an impenetrable wall. Collins' constituents are about as far as you can get from the Rio Grande, and they have not been overrun by Mexican immigrants, legal or otherwise. Hispanics of all types make up just 2.6 percent of the population there.

Trump's ability to inflame such passions in so many places is puzzling because the number of foreigners coming here illegally has been declining. The number living in the United States is down by nearly 1 million from the 2007 peak. The volume of apprehensions by the Border Patrol along the border with Mexico has plunged.

Fear of terrorism has something to do with this urge to seal off the southern border. Republican presidential candidates have raised the terrifying specter of Islamic State terrorists sneaking into the country from Mexico.

None of them mentions that the 9/11 hijackers came here legally. Nor does anyone seem to recall that in 2011, the head of Customs and Border Protection said, "We have had more cases where people who are suspected of alliances with terrorist organizations or have had a terrorist suspicion in their background -- we see more people crossing over from Canada than we have from Mexico."

Oddly, Trump pays no attention to our northern frontier. Something about Canada just doesn't frighten people -- even people who can see Toronto from their homes -- the way Mexico does.

Trump is fond of saying that the southern border is so porous as to be no border at all. "If we don't have a border, we don't have a country," he asserts.

As a matter of history, he couldn't be more wrong. "The Mexico-U.S. border remained little more than a line on a map, entirely unguarded by federal authorities until 1924, when the U.S. Border Patrol was established," writes Princeton sociologist Douglas Massey. Ronald Reagan, the hero of every Republican, envisioned a North America without border controls.

It's not just illegal immigration that alarms Trump fans. Sen. Jeff Sessions, R-Ala., who endorsed him this week, favors a reduction in legal immigration. So does the Federation for American Immigration Reform, which has praised Trump's immigration plan. "I'm opposed to new people coming in," he said in 1999.

Racial prejudice undoubtedly motivates many of his supporters. One thing Mexicans and Central Americans sneaking over the southern border usually have in common with Middle Eastern refugees is a dusky complexion.

That doesn't win them points with the 70 percent of Trump voters in South Carolina who think the Confederate flag should still be flying at the state Capitol or the 16 percent who believe "whites are a superior race."

UCLA political scientist Lynn Vavreck has documented that many of his supporters are "people who are responsive to religious, social and racial intolerance." Latinos and Muslims get the blunt end of their response.

It clearly infuriates those drawn to Trump that they have repeatedly failed to get their way on the issues they are passionate about. Most Americans, polls show, are in favor of giving unauthorized immigrants a path to citizenship. Most think immigrants strengthen America. Most want to let those brought here illegally as children gain legal status. Most are fine with the country's becoming browner and more culturally diverse.

On these and other matters, Trump's supporters have been losing, year in and year out. That's not the fault of corrupt Washington insiders or cowardly politicians or weak leadership. They have been losing because the majority of Americans have considered their views and rejected them.

The fantasy Trump holds out to his followers is that despite being out of step with the majority of their fellow Americans, they can dismantle all the changes they detest. Win or lose, they're in for a disappointment.